Automatically-powered gas-operating mechanisms for firearms are well known in the prior art. These systems allow for the extraction, ejection, and loading operations to be performed automatically by tapping into the energetic gases generated by the chemical reaction of the propellants used to accelerate the projectile.
These systems typically tap into the barrel to vent a portion of the gas used to propel the bullet and divert that gas flow to impinge on a piston which drives the mechanism. Traditional systems use a short length of porting to direct the gas to impinge upon the piston. The piston is then linked via an operating rod to the bolt carrier which then in turn operates the bolt to perform. These systems are generally referred to as gas-piston operating systems.
The typical piston gas-operating system taps into a forward section of the barrel to reduce gas pressure and temperature since both these factors are reduced as the distance from the chamber increases. The type of system is well proven in ubiquitous designs such as the AK47 and FN-FAL. Benefits of the system include relative cleanliness and ease-of-maintenance since combustion byproducts and un-burnt powder are concentrated in one area which is removed from other parts of the operating mechanism. However, detractions of this system are evident since the piston is located in a forward position and must be linked via a long operating rod to the firearm mechanism. This increases muzzle weight (which is already heavily affected by modern rail-mounted accessories), increases off-axis forces which can reduce both inherent accuracy due to barrel flex and user accuracy due to muzzle rise or other induced moments. There is also an inherent instability caused by the imbalance of the system.
A direct impingement system was developed in 1956 by Eugene Stoner. It uses a gas tube that acts on the bolt carrier itself while it acts on a piston contained inside the bolt carrier. Gas is routed into the bolt carrier, where pressure builds against the locked bolt and pushes the bolt carrier to the rear to unlock the bolt. The gas tube is then disconnected from the carrier, and the action is cycled as the bolt and carrier travel rearwards. The M-16 rifle, commonly used in the U.S. military, utilizes this system.
This direct impingement gas system has the advantage of reducing the amount of moving mechanism and weight towards the front of the weapon. This generally improves balance and handling. Additionally this system allows for an inline operating system where the piston impinges coaxially with the bore axis. This reduces the amount of torque moments on the barrel and the weapon that may be induced by an operating system that drives a non-coaxial piston and can improve accuracy both inherent in the weapon and reduce muzzle climb or other weapon rotation thereby increasing user accuracy. Rate of fire and dwell time can also be improved in this system since the gas must pressurize a larger volume inside the gas tube and travel a longer distance within that tube in order to impinge upon the piston and operate the mechanism. Overall this system offers improvement in both fully-automatic fire and improving dwell time for optimal function. However, direct impingement introduces an excessive amount of un-burnt powder residue and combustion by-products into the core operating mechanism of the weapon such as the fire-control group. For the user this means that extra cleaning and maintenance must be performed to keep the weapon operating at optimal reliability levels.
Due to the limitations of both direct impingement and gas-piston operating systems the need for an improved system that mitigates the negative effects of each of these systems is apparent.
The new system disclosed is a hybrid gas system which integrates many of the advantages of both traditional gas-piston and direct-impingement operating systems. A direct-impingement type gas tube is used to tap into a forward section of barrel and allows the energy of the tapped gases to be redirected to power the mechanism without introducing a long and heavy operating rod. Since traditional gas-piston systems use a cylinder and piston system mounted toward the end of the weapon, a reinforced operating rod must be used to transmit linear force to the bolt carrier without buckling under compressive loads. By eliminating this part and replacing it with a lightweight gas tube, the muzzle weight is reduced.
Unlike the direct impingement system, this tube directs the gas rearward to impinge upon a piston contained within a cylinder directly mounted to the trunnion. This retains the cleanliness advantage of gas-piston systems since the piston and cylinder are removed from the bolt carrier and are separated from the fire-control group by the trunnion. This significantly reduces the amount of fouling and debris able to contaminate the firing mechanism firing unlike direct-impingement systems. Additionally torque inducing moments near the end of the barrel may be reduced since the piston mechanism is more rigid in the trunnion structure than on the cantilevered barrel which can bend on typical gas-piston systems.
While other operating systems exist that mount the piston in close proximity to the receiver, this hybrid system is different than others such as the Benelli ARGO system for the M1018 and M4 Super 90 shotguns which tap the gas closer to the chamber and would not be suitable for a rifle. Piston systems for rifles usually have a piston operating near the gas block towards the end of the barrel again to tap into a lower pressure part of the barrel and allow for some additional dwell time in-order to allow the cartridge case to extract efficiently.
Due to the physical layout and arrangement of the system, clear advantages can be obtained in select fire controllability, reduction in rate-of-fire, improved cycle and dwell time for cartridge case extraction, improved weight distribution, user maintainability, reliability and better structural rigidity.